Field of Invention
The present invention relates to a hydraulic testing system in the field of electromechanical control, and, in particular, to a same-time-domain multi-frequency band hydraulic testing system and control method thereof.
Description of Related Arts
A conventional complete hydraulic testing system, according to the block schematic diagram, is formed of five portions, which are data processing system, control system, executive system, load, and measuring system. Input command signal is identifiable computer program language translated from the test plan for the hydraulic testing system. The input command signal is utilized for commanding the acts of the hydraulic testing system. The data processing system processes the input command signal and data from the measuring system and commands the acts of the control system. The control system in the hydraulic system control and adjust the pressure, current capacity, and direction of the fluid. The executive system converts the pressure energy of the fluid into mechanical energy to drive the load to conduct straight line reciprocal motion or rotation. The load is the response of the hydraulic testing system and usually is the response of the test subject to the input command signal. The measuring system is to measure the response of the hydraulic testing system and to serve as feedback. The minimum frequency of hydraulic system (fmin) is the control frequency that is usually determined by the frequency characteristics of the electrohydraulic servo valve of the control system. Besides, the test frequency and data processing frequency of the hydraulic system may both be higher than the control frequency of the system (fmin). A hydraulic testing system mainly includes two parts, which are hydraulic system and test subject. When the testing system is utilized in the field of civil engineering, if a compression and tensile test is conducted on concrete, high-strength concrete, and ultra-high strength concrete, it usually obtains a stress-strain curve, while if a stress-strain complete process curve (complete curve hereinafter) test is conducted on rock, high-strength concrete, and ultra-high strength concrete, a complete curve is usually expected to be obtained. Stress-strain curve and complete curve are two of the most basic characteristic curves to research materials mechanics properties. It can even apply the law of conservation of energy to analyze the interrelations among the stress-strain curve, the complete curve, and the hydraulic testing system. Stress-strain curve test and complete curve test are usually independently completed in a hydraulic testing system. Because brittle failure occurs on concrete, especially high-strength concrete and ultra-high strength concrete in compression and tensile test, but the measurement frequency of the measuring system in the hydraulic testing system (static measuring system hereinafter) is not high enough, the full view of the characteristics of the stress-strain curve and complete curve can not be adequately described. Some adds a dynamic stress strain measuring system (dynamic measuring system hereinafter) besides the conventional hydraulic testing system to independently collect data. Then the stress-strain curve or complete curve can be obtained by the data processing afterward. Unfortunately, because the dynamic measuring system and the hydraulic testing system are two independent systems, the dynamic measuring system can not feedback for the controlling of the test and the data processing afterward can not guarantee enough accuracy as well.
A complete hydraulic testing system, according to its composition and structure, is formed of six portions, which are power system, data processing system, control system, executive system, auxiliary system, and hydraulic fluid. The power system turns the mechanical energy of the prime motor into the pressure energy of the fluid. The data processing system processes the input command signal and data from the measuring system and commands the acts of the control system. The control system controls and adjusts the pressure, current capacity, and direction of the fluid in the hydraulic system. The executive system converts the pressure energy of the fluid into mechanical energy to drive the load to conduct straight line reciprocal motion or rotation. The auxiliary system mainly comprises the fuel tank, oil filter, oil tube and pipe connector, sealing ring, quick change connector, etc. The hydraulic fluid is the actuating medium that transmits energy in the hydraulic system. The minimum frequency of hydraulic system (fmin) is the control frequency that is usually determined by the frequency characteristics of the electrohydraulic servo valve of the control system. Besides, the test frequency and data processing frequency of the hydraulic system may both be higher than the control frequency of the system (fmin). The opening of the valve of the control system has two types in terms of continuity, which are two states (completely opened and completely closed) and continual opening. The description of degree of valve opening can be in two ways, which are in relative value and in absolute value. For example, the valve opening of the completely closed state is zero for both descriptions of relative value and absolute value, while the valve opening of the completely opened state is 100% in relative value and 1, 100, or other positive integer greater than 100 in absolute value.
When hydraulic system suddenly starts, stops, changes speed, or reverses, the valve port will suddenly close or stop. Nonetheless, because of the inertia of the flowing fluid and moving parts, there will be a very high peak pressure instantly generated in the system, which phenomenon is called hydraulic impact. When hydraulic impact occurs, the peak value of the partial pressure change in the system may reach several times of the regular functioning pressure value. Therefore, it is extremely likely to render vibration of the system and possibly to cause seal breakage, pipeline burst, or weld line crack that trigger oil leakage in the system. Besides, it can bring manometer and flowmeter fail, pressure relay and sequence valve misssend signal, pressure regulating valve and flow valve break. Moreover, it may even lead the load of the concrete sample (component) to attain the ultimate load and scrap the sample (component). Hydraulic impact not only influences the reliability of the hydraulic system itself, but also cracks or scraps the concrete sample (component) or possibly causes secondary impact to the personnel and environment.
The limitations of conventional hydraulic testing system includes:
1. Because the measurement frequency of the measuring system in the conventional hydraulic testing system is not high enough, when a hydraulic testing system is solely employed to conduct a stress-strain curve test and a complete curve test, it can not fully describe the characteristics of the stress-strain curve and complete curve. Adding a dynamic measuring system outside of a conventional hydraulic testing system to independently collect data is another option. Unfortunately, because the dynamic measuring system and the hydraulic testing system are two independent systems, the dynamic measuring system can not feedback for the controlling in the test and the data processing afterward can not guarantee enough accuracy as well.
2. Conventional hydraulic impact preventions and treatments are mostly focusing on providing physical improvements of the power system, control system, executive system, auxiliary system, and hydraulic fluid of the hydraulic system, while there is still not enough improvement on control method and the hydraulic impact problem is not completely solved yet.